In early December 2019, an outbreak of the novel coronavirus pneumonia (COVID-19) occurred in Wuhan, Hubei Province, China, and spread fast throughout China. As of 15 June 2020, there have been about 84,000 confirmed cased over China. The Chinese government launched a national emergency response upon the detection of the COVID-19 in Wuhan. To curb the spread of the epidemic, the outbound channels of Wuhan have also been closed since 23 January 2020 (Li et al. 2020; China Internet Information Center 2020). On 26 January, the second day of the Chinese Lunar New Year, all motor vehicles were banned in urban central Wuhan, except for special vehicles to supply epidemic prevention (Hubei Government 2020). In terms of the national prevention and control measures, the government encouraged people to stay at home; discouraged mass gatherings; extended the Lunar New Year holiday; closed all crossprovince bus services; and closed schools, government offices, and factories (Chen et al. 2020).
The nationwide antivirus battle in China brought great changes to personal daily life and society operation, and caused a huge challenge to some sensitive sectors, including transportation, tourism, retail, and entertainment, which lead to GDP decreasing by 6.8% in the first quarter of 2020 (National Bureau of Statistics 2020). But on the other hand, many regions in China have been suffering from severe air pollution in recent years. A drastic drop of air pollutant emissions occurring with the national lockdown improved the human living environments greatly (Patel 2020). The nationwide lockdown can be considered as an ideal and unique field experiment for the prevention and control of current severe air pollution. It is still unclear how the air quality changes during the lockdown period and what we should learn about air pollution mitigation from this nationwide ideal experiment.
Daily mean air pollutant concentration observations were obtained from the website of the Ministry of Ecology and Environment of China (http://220.127.116.11:20035). The four-times-daily ERA5 dataset from December 2013 to March 2020 was downloaded from www.ecmwf.int/en/forecasts/datasets/reanalysis-datasets/era5. This study was supported by the National Natural Science Foundation of China (41790470 and 41805117).
Appendix: Air Pollutant Concentrations during the COVID-19 Outbreak Versus the Historical Average
Figure A1 shows the air pollutant concentrations during BF, AF1, and AF2 as well as their historical average. The historical average over most of the listed provinces shows notable monthly variation from His_BF to His_AF2, with the concentrations of particulate pollutants, SO, CO, and NO2 decreasing and the O3 concentration increaseing gradually.
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